It is our goal to determine the mechanisms of interaction between two lungs of different sizes and mechanical properties. Our preliminary observation that the distribution of inspired gas between an emphysematous lung (E) and a normal lung (N) varies substantially with the mode of breathing caused us to consider the implications of these mechanisms for single lung transplantation. We will determine how lungs of unequal sizes and mechanical properties deform the chest wall and will characterize the consequences of this deformation on regional ventilation and the function of the respiratory pump. Using biplane fluoroscopic marker techniques, we will image the lungs and hemi-diaphragms of dogs with unilateral papain-induced emphysema and test the following hypotheses: (1) during mechanical ventilation at conventional rates, most of the inspired gas is distributed to the E lung because it is more compliant; (2) during spontaneous breathing, most of the inspired gas is distributed to the N lung because the displacement of the hemi-diaphragm which apposes the N lung is greater than the displacement of the hemi-diaphragm which apposes the E lung; and (3) differences in shape and preload (length of muscle fibers prior to activation) cause the hemi-diaphragms to displace by different amounts. To relate displacement to muscle mechanics, we will quantify all determinants of shortening, which are intrinsic to the hemidiaphragms and consist of preload, contractile state, and afterload. On the basis of these measurements, we will determine if systematic differences in hemi-diaphragm lengths and shortenings are consistent with uniform loads and neural activation.